The present invention is drawn to an amplifier and a processing system enabling a submersible vehicle to accurately determine its location.
Conventional methods employed by submersible vehicles to determine their location when submerged are prone to inaccuracies or unreliable. More accurate methods used when on the surface are not available when submerged below periscope depth.
One conventional method submersible vehicles use for determining their location is with inertial guidance systems. Inertial guidance systems operate by monitoring acceleration and changes in rotational attributes like pitch, roll and yaw. This data along with the submersible vehicle's speed is processed by a computer to determine the current position of the submersible vehicle. Unfortunately, inertial guidance systems suffer from accumulated error. Any errors in measurement of the rotational attributes are accumulated. With enough error accumulation, the total error can become significant enough to cause safety issues as the operators of the submersible vehicle think they are at a particular location, but are actually at a very different location.
Submersible vehicles have several other methods for navigation including sonar, radar, radio and Global Positioning System (GPS). Each of these methods has limitations with respect to their use. Submersible vehicles may operate in stealth mode wherein active sonar and radar methods of navigation may not be used because such methods may enable outside observers to determine the location of the submersible vehicle. Submersible vehicles can determine their location with radio navigation and a GPS, however both of these methods require the submersible vehicle to operate at periscope depth and extend an antenna above the surface of the body of water.
FIG. 1A illustrates a conventional method in which a submersible vehicle is able to determine its location using a GPS.
FIG. 1A includes a submersible vehicle 100 under the sea surface 102 within an undersea region 116. Submersible vehicle 100 includes a periscope 104 and an antenna 106. A GPS satellite 108 provides a radio signal 110, whereas a GPS satellite 112 provides a radio signal 114.
The majority of submersible vehicle 100 is located in undersea region 116. Periscope 104 and antenna 106 extend above the upper region of submersible vehicle 100. When submersible vehicle 100 is at periscope depth, as illustrated in FIG. 1A, it is able to use periscope 104 by extending it above sea surface 102. Submersible vehicle 100 uses periscope 104 to view objects located on or adjacent to sea surface 102. At periscope depth, submersible vehicle 100 is able to extend antenna 106 above sea surface 102. When antenna 106 is extended above sea surface 102, antenna 106 is able to receive radio signal 110 and radio signal 114. GPS satellite 108 and GPS satellite 112 are located in orbit above the earth. Submersible vehicle 100 is able to process radio signal 110, and radio signal 114 to determine its location.
FIG. 1B illustrates submersible vehicle 100 when it is below periscope depth and is not able to determine its location using a GPS.
As illustrated in FIG. 1B, submersible vehicle 100 is fully submerged beneath sea surface 102. Antenna 106 is positioned beneath sea surface 102 and is located in undersea region 116. Due to their high frequencies, radio signal 110 and radio signal 114 are not able to penetrate into undersea region 116, where antenna 106 is located. Submersible vehicle 100 is not able to receive radio signal 110 and radio signal 114 and is not able to determine its location.
A conventional method for a submersible vehicle to determine its position, while below periscope depth, using GPS satellites will now be described with reference to FIG. 2.
FIG. 2 illustrates a conventional method for a submersible vehicle to determine its location using a GPS and a buoyant cable antenna (BCA).
FIG. 2 includes submersible vehicle 100 under the sea surface 102 within an undersea region 116. Submersible vehicle 100 includes has a BCA 202 attached thereto. BCA 202 includes a buoyant transmission cable portion 204 and an inline amplifier 206, and a buoyant antenna portion 203. GPS satellite 108 provides radio signal 110, whereas GPS satellite 112 provides radio signal 114.
As illustrated in FIG. 2, submersible vehicle 100 is fully submerged with antenna 106 and periscope 104 located in undersea region 116. As described previously and illustrated in FIG. 1B, antenna 106 is not able to receive GPS radio signals 110 and 114. As a result, submersible vehicle 100 is unable to determine is location with a GPS using antenna 106.
However, the buoyant antenna portion 203 of BCA 202 floats on sea surface 102 while the other end is connected to submersible vehicle 100. Since buoyant antenna portion 203 floats on top of sea surface 102, it is able to receive radio signal 110 and radio signal 114. Radio signal 110 and radio signal 114 would be conveyed from BCA 202 to submersible vehicle 100. Inline amplifier 206 would be required to amplify radio signal 110 and radio signal 114 to account for losses while traveling along buoyant transmission cable portion 204. Submersible vehicle 100 receives the amplified version of radio signal 110 and radio signal 114. Submersible vehicle 100 uses the amplified version of radio signal 110 and radio signal 114 to determine its location with a GPS. However two problems still exist with this method.
The above described method determines the location of buoyant antenna portion 203. Only an approximate location of submersible vehicle 100 is determined as a result of the distance between an end of BCA 202 and submersible vehicle 100 as denoted by a separation distance 210.
A second problem with the above method is that conventional inline amplifier 206 is not capable of providing sufficient amplification of radio signal 110 and radio signal 114 to reach the interior of submersible vehicle 100 with sufficient strength to be used to determine a position.
An example conventional inline amplifier 206 will now be described with reference to FIG. 3.
As illustrated in FIG. 3, inline amplifier 206 includes a filter 300, an amplifier 302, a gain compensation filter 304, an amplifier 306 and a filter 308.
Filter 300 is arranged to receive an input signal 310 and output a filtered signal 312. Amplifier 302 is arranged to receive filtered signal 312 and output an amplified signal 314. Gain compensation filter 304 is arranged to receive amplified signal 314 and output a compensated signal 316. Amplifier 306 is arranged to receive compensated signal 316 and output an amplified signal 318. Filter 308 is arranged to receive amplified signal 318 and output an output signal 320.
In operation, the end of BCA 202 receives a signal, for example from GPS satellite 108. The signal is transmitted along buoyant transmission cable portion 204 until it is amplified by inline amplifier 206. Specifically, filter 300 receives input signal 310 and passes a portion of input signal 310 that is within a predetermined frequency band(s) of interest and attenuates the remaining portions of input signal 310.
Amplifier 302 amplifies filtered signal 312.
Gain compensation filter 304 compensates for the signal attenuation characteristics of the transmission cable connected between output of inline amplifier 206 and submersible vehicle 200. Specifically, gain compensation filter 304 has a transfer function that provides an incremental increase in amplification for a predetermined portion of amplified signal 314.
Amplifier 306 amplifies compensated signal 316.
Filter 308 receives passes a portion of amplified signal 318 that is within a predetermined frequency band(s) of interest and attenuates the remaining portions of amplified signal 318.
As discussed above, even if BCA 202 is able to transmit received GPS signals to submersible vehicle 100, submersible vehicle 100 may not accurately determine its location as a result of the unknown position of buoyant antenna portion 203 relative to submersible vehicle 100.
What is needed is a system and method for a submersible vehicle to accurately determine its location when submerged.